Iran said today it had busted past limits on its stockpiles of uranium. Those limits were set under the 2015 nuclear deal with the U.S. and other nations. The White House says Iran, quote, "must end its nuclear ambitions." We're going to compare that demand with the more measured approach to another nuclear power, North Korea. First, NPR's Geoff Brumfiel looks at whether this is the start of a new nuclear crisis in the Middle East.

GEOFF BRUMFIEL, BYLINE: The deal was supposed to be simple. Iran would freeze some parts of its nuclear program and roll back others in order to keep it about a year away from getting enough uranium to make a bomb. And in exchange, it would get relief from economic sanctions. But that was before the U.S. pulled out.

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PRESIDENT DONALD TRUMP: I am announcing today that the United States will withdraw from the Iran nuclear deal.

BRUMFIEL: That was President Trump speaking last May. The U.S. has reimposed sanctions and added new ones. And now Iran is walking back its side of the bargain one bullet point at a time. Today it announced it has surpassed a 300-kilogram limit on low-enriched uranium. Ali Vaez with the International Crisis Group says that number is somewhat arbitrary.

ALI VAEZ: The fact that Iran has produced more low-enriched uranium than the deal allows by a few kilograms doesn't mean that the sky is going to fall.

BRUMFIEL: The uranium is only enriched to about 3.5%. It cannot be used for a bomb. But Vaez says that Iran soon plans to cross other lines set in the deal.

VAEZ: They have threatened, as of July 7, to start enriching at higher levels, like 20%, which is much closer to the weapons grade of 90%.

BRUMFIEL: And that could mean, by the end of the summer, Iran would begin to reduce the time it needs to get uranium for a nuclear weapon - although Iran's official line is that its program is peaceful.

Why is this happening now? Mahsa Rouhi at the International Institute for Strategic Studies says that a lot of it has to do with the tough position Iranian President Hassan Rouhani finds himself in.

MAHSA ROUHI: We always talk about how President Trump has to keep the campaign promises. But we often tend to forget that President Rouhani is under very similar pressure by not only the hard-liners but also the public opinion.

BRUMFIEL: Iran's nuclear program is very popular domestically. Rouhani won election on the promise that freezing it would improve the economy. So far, he hasn't been able to deliver.

ROUHI: People are left thinking - well, now we have basically accepted the limits on our nuclear program. Why are we still being punished?

BRUMFIEL: Today's announcement by Iran is aimed squarely at European powers who are still in the deal. By crossing these lines, Iran is hoping it can pressure Europe to come up with the economic benefits it was originally promised. Europe is working to provide some humanitarian aid - things like medical supplies. But Ali Vaez says it won't be enough to satisfy Iran.

VAEZ: Nothing that Europe would do on its own in the next few months would constitute a silver bullet for the Iranian economy.

BRUMFIEL: Vipin Narang, a political scientist at the Massachusetts Institute of Technology, says it appears almost inevitable that Iran will follow through and ramp up its nuclear program again, even as Washington warns it not to.

VIPIN NARANG: It's unclear how the administration will respond to that.

BRUMFIEL: Narang says Iran is also probably paying attention to events in North Korea. That nation decided to build nukes despite sanctions. This weekend, President Trump met with North Korean leader Kim Jong Un. Iran is watching, Narang says.

NARANG: The red carpet treatment that Kim Jong Un gets and the love letters - they're thinking it's good to be a nuclear weapons state.

BRUMFIEL: As of today, Iran is still over a year away from getting a bomb - if it decides to. But that timeline looks likely to start shrinking soon.